The library at the University of Illinois at Chicago has just released a series of photographs of downtown Chicago street scenes taken by the Illinois Department of Transportation over the years. Being the IDOT, there are admittedly many photographs of empty intersections, but among them are plenty of the sort of photographs a lot of us could spend a pleasant afternoon browsing.

To whet your appetite, here’s one I like. Taken at the intersection of Sheridan, Montrose and Broadway on a late June afternoon, let’s see if you can peg the year; then see what you can spot in the traffic. Click on the image for a hi-res version, and there’s an even larger one here.

If you’re stumped, click through for the answer here.